JPS6224222A - Optical wavelength varing device - Google Patents

Abstract

PURPOSE:To decrease the number of parts of a constituent device, and to obtain an optional wavelength by using a high output laser which becomes a pump light, and a double refraction fiber or a polarized wave holding fiber, and changing an oscillation wavelength by an intensity of a high output laser beam. CONSTITUTION:The titled device is constituted by combining an Nd:YAG laser 1, an attenuator 2, a lambda/4 plate 3, a polarizer 4, a lens 5, a double refraction fiber or polarized wave holding fiber 6, and a wavelength branching device 7 of a grating or a prism or a monochromator, etc. A YAG laser beam which is controlled by a mode lock Q switch goes to excitation light and set to an optional intensity through an optical attenuator 2, goes to linearly polarized light through the lambda/4 plate 3 and the polarizer 4, and made incident on an axis whose refractive index is higher, in each orthogonal optical axis of the double refraction fiber or polarized wave holding fiber 6. Length of the double refraction fiber or polarized wave holding fiber 6 is several (m) through scores of (m), and a long fiber is not always required for generating stokes light and anti-stokes light by mixing four induction photons.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pulse generator using an optical fiber used in coherent optical transmission and sensor technology using an optical fiber.

[Conventional technology]

Conventionally, harmonization and difference frequency conversion has been performed using a powerful laser beam and utilizing the anisotropy of various crystals (for example, bluestite). A parametric frequency conversion method using this type of crystal requires control of the crystal temperature and the angle of incidence of incident light, and has the drawback of requiring a large number of parts and complicating the device configuration. In addition, the stimulated Raman scattering method uses Stokes light generated by Raman scattering. 7 dopant materials such as
Is it necessary to change the natural oscillation mode by putting it in the TABA? Because its wavelength variable range is small, it is 43 μm.
On the short wavelength side of the above continuous oscillation region, there is a drawback that it is difficult to freely change the oscillation wavelength.

[Problems and solutions to be solved by the invention] The present invention uses a high-output laser serving as a so-called pump light and a birefringent birefringent or polarization-maintaining fiber to change the oscillation wavelength depending on the intensity of the high-output laser beam. Its purpose is to reduce the number of component parts and to obtain an arbitrary wavelength.

〔Example〕

Figure 1 shows an embodiment of the present invention, where l is a Nd:YAG laser, c is an optical attenuator, J is a 2/4 plate, d is a polarizer, j is a lens, and t is a birefringent fiber or polarized wave. Hold 7 Aipa,
7 is a wavelength demultiplexer such as a grating, a prism, or a monochromator. In this example, YAG laser light controlled by a mode-locked Q-switch is used as excitation light, which is passed through an optical attenuator to a desired intensity, and then passed through an air plate and a polarizer as linearly polarized light. Among the optical axes to be used, the light is incident on an axis with a high refractive index (hereinafter, the direction of the axis with the higher refractive index is taken as the X-axis, and the axis with the lower refractive index is taken as the y-axis in a coordinate system). The length of the birefringent 7-fiper or the polarization-maintaining 7-fiber is from several meters to several tens of meters, and since one Stokes light and one anti-Stokes light are generated due to photon mixing, a long 7-fiber is not necessarily required.

Next, the operating principle of the apparatus of the present invention will be explained. The following phase matching conditions are required to generate a wavelength different from the excitation light through stimulated photon mixing.

k, +, -2kp=o (1
) Here, ks and kA are wave vectors of Stokes light 9 and anti-Stokes light, respectively, and k is a wave vector of excitation light. This phase matching condition is approximately given by the following equation using the mismatch amount Δk (ΔrI) with the frequency shift amount Δ; in the glass material and the mismatch amount f (Δma) due to mode dispersion and mode birefringence.

Δk(Δma)+f(Δ;＞=o (
2) That is, Stokes light and anti-Stokes light are generated at a frequency shift amount Δ that satisfies equation (2). When the phase matching conditions are met, equation (2) can be expressed as follows.

f(Δν)=−2CNx−N, )C2π et al.)=−J (
Bg + Bs ) (Jπ:p> (8)
=-JBo (πνp) Here, Nx and Ny are the effective refractive indices of the X-axis and y-axis, respectively; p is the normalized frequency. Bg is mode birefringence caused by the structure, and B5 is stress birefringence caused by stress remaining in the optical 7 eyer.

The N2 diagram shows the calculated value of the phase matching amount Δk (Δ;) for fused silica. In Figure 2, the curve of Δk(Δi) and -,
Δ; at the intersection of f (Δi) gives the frequency shift amount.

Therefore, if Bg or B$ is changed in equation (3).

Δ; will change.

As in this embodiment, a YAG laser controlled by mode locking and a Q switch can obtain a light intensity of about IO'W. When such strong light enters the fiber, the light K
The refractive index changes in proportion to the light intensity due to the err effect. The amount is given by the following formula.

Nx-N, = (Nx, -N,.)+H(Px-Py
) (4)=Bo+H(Px-Py) where s NX0m N)'. are the effective refractive indexes when no light is incident, * px and p are the X-axis, respectively.

In the y-axis light intensity, X is the self-focusing coefficient of the optical Kerr effect, /, /X10 esu. In this example, Py=
Set to 0. Equations (8) and (4) The amount of phase mismatch f(Δi) due to sysmode birefringence and mode dispersion is expressed by the linear formula % Formula % In this way, f(Δ;) depends on the incident intensity P.
′ becomes.
1. That is, by changing the incident intensity,
It can be seen that the wavelength of the Stokes light 1 anti-Stokes light can be changed. Figure 3 shows the incident intensity P&C.
! Oscillation of Stokes light and anti-Stokes light for
゛The relationship between wavelengths is B. The results calculated for a fiber with =i, zxio are shown. From now on, the incident light intensity P=#
)'W, one frequency shift J ν= 7 Q 1m-
'shifted from the excitation light, i.e. wavelength 06 tat μm and/
, / j /μm different lights are obtained by the stimulation≠photon effect.

〔Effect of the invention〕

As explained above, the device of the present invention has the advantage that the oscillation wavelength can be varied depending on the intensity of the incident light, and the structure of the device is simple, so that it can be applied as a wavelength tunable light source to optical communication systems and optical cell technology.

[Brief explanation of the drawing]

Figure 1 shows an example of the present invention, and Figure 2 shows the amount of mismatch Δk (Δ;) of the glass material with respect to fused silica and the amount of frequency shift Δ.
Figure 3 is a diagram showing the relationship between the variable wavelength range obtained by the present invention and the incident light intensity.〇λ l...Nd: YAG laser, 2... Optical attenuation vessel,
3...-reef plate, ≠... polarizer, j... lens, t... birefringent 7-eye fiber or polarization maintaining fiber, 7... wavelength demultiplexer.

Claims (1)

[Claims] It consists of a high-power laser light source, an optical system that converts the laser light from the light source into linearly polarized light, a birefringent fiber, and a wavelength demultiplexer, and converts the laser light from the light source into linearly polarized light. 1. An optical wavelength tunable device, characterized in that the light enters the birefringent fiber so as to coincide with the high axis, and the output light from the birefringent fiber is demultiplexed by the wavelength demultiplexer to obtain light of a desired wavelength.